Environmental sealing

ABSTRACT

A method of forming a branch-off seal between a heat-shrinkable sleeve and at least two spaced-apart elongate substrates, which comprises the steps of: 
     (a) positioning the substrates within the heat-shrinkable sleeve; 
     (b) positioning between the substrates and within the sleeve at an open end thereof a plug having a larger cross-sectional size at a first position away from said open end and a smaller cross-sectional size at a second position towards said open end; 
     (c) positioning a heat-activatable sealing material at the first position; 
     (d) shrinkable conduits in the sleeve by positioning one or more clips at the open end of the sleeve such that the substrates and the plug are in respective conduits; and 
     (e) while the clip remains on the sleeve, applying heat so as to affect shrinkage of the sleeve to activate the sealant, and form the desired seal.

This invention relates to environmental sealing, particularly by meansof a heat-shrinkable sleeve of substrates, such as telecommunications orother cables, particularly at cable splices or other regions wherecables run close to one another, especially spaced apart by a fixedamount.

Heat-shrinkable articles are now widely used in many areas whereenvironmental sealing, for example, insulation, bonding orencapsulation, is required. Usually these articles dimensionally-recoveron heating to a shape from which they have previously been deformed, butthe term "heat-shrinkable" as used herein also includes an articlewhich, on heating, adopts a new configuration, even if it has notpreviously been deformed.

In their most common form, such articles comprise heat-shrinkablesleeves made from polymeric material exhibiting the property of elasticor plastic memory as desired, for example, in U.S. Pat. Nos. 2,027,962,3,086,242 and 3,957,372.

Heat-shrinkable sleeves find many applications, especially in theconnection and termination of wires, cables and pipes. However, thereare applications where it is desirable to provide a sealing member forelongate substrates such as cables or pipes or other supply lines whoseends are not accessible. For such applications so-called "wrap-around"sleeves have been developed. Basically, they are heat-shrinkable sheetswhich can be wrapped around a substrate to form a generally tubularshape and which, in general, are provided with fastening means forholding them in the wrapped-around configuration during heat-shrinkage.Examples of such sleeves are disclosed in GB1155470.

Heat-shrinkable sleeves have been successfully employed in many fields,but problems may arise when two or more substrates have to be sealed atone position. This problem, which is known as "branch-off", may occur,for example, at the outlet of a heat-shrinkable part. Amongst fields inwhich this problem is typically encountered there may especially bementioned the outlets of the splice cases described and claimed inGB1431167 (Raychem), the disclosure of which is incorporated herein byreference.

One effective solution for tubular sleeves has been to use mouldedheat-shrinkable parts provided with preformed outlets for the individualsubstrates. However, in general, such parts have to be made to suit aparticular application, and many different such parts will therefore berequired to cover all the applications likely to be encountered.

A solution of major commercial importance to this problem is disclosedand claimed in U.S. Pat. No. 4,648,924 (Raychem), the disclosure ofwhich is incorporated herein by reference. In that patent, a method offorming a branch-off seal between a heat-shrinkable sleeve and at leasttwo substrates, comprises the steps of:

(a) positioning the substrates within a heat-shrinkable sleeve;

(b) forming at least two heat-shrinkable terminal conduits bypositioning a clip having at least two elongate legs over the outersurface of the heat-shrinkable sleeve at an open end thereof, wherein atleast two of said legs are positioned externally of the sleeve and thesubstrates are within the terminal conduits; and

(c) while the clip remains on the outer surface of the heat-shrinkablesleeve, applying heat so as to effect shrinkage of the sleeve and toform the desired seal.

U.S. Pat. No. 4,400,579 (Raychem) discloses and claims an assemblycomprising a heat-shrinkable sleeve capable of being positioned aroundat least first and second elongate substrates, and a clip formed as atrident, the outer legs of which are capable of being positioned overthe outer surface of the sleeve at the end thereof with the central legof the trident (which may taper towards its proximal end and may becoated with an adhesive) inside the sleeve so as to form, and maintainduring subsequent heat shrinkage of the sleeve, at least two terminalconduits respectively capable of receiving the first and secondsubstrates.

Whilst the clips disclosed in these patents are outstandingly successfulfor most uses, some difficulties may be noticed under unfavourableconditions, for example, where the distance between the substrates issignificant and cannot be altered. For example, in some countries it iscommon to enclose a telephone cable splice in a lead box which isprovided with spaced apart lead conduits for the incoming and outgoingcables. The cables may vary in diameter between, say, 18 and 95 mm andthe distance between the conduits may be fixed at, say, 30 mm. In such asituation gaps would remain under the sleeve even if several clips wereused.

An attempt to solve this problem is related in GB 2019114 (Raychem)which discloses and claims a kit of parts comprising a heat-shrinkablesleeve and at least one fork member for use in forming a seal betweenthe sleeve and at least two substrates by a method which comprisesthreading an end portion of the sleeve, which is positioned between thetwo substrates about the prongs of the fork member so that, on recovery,the heat shrinkable material tightens within the prongs of said forkmember and at least two of the prongs of the fork member abut the outersurfaces of the sleeve surrounding the substrate so as to retain thefork member firmly in position, the fork member being retained withlateral ears that in use may rest against substrates where they pass outof the sleeve.

A tubular clip having longitudinally-extending,circumferentially-separated slits is disclosed in EP 0094793 (Raychem).The intention there is to hold together two thicknesses of aheat-shrinkable sleeve between two spaced apart substrates.

Reference may also be made to EP 0050995 (Raychem) which discloses theuse of two or more clips (one of which may be a heat-pipe) to seal aheat-shrinkable sleeve around three or more cables, and also to DE2413623 (Rose) and DE 3243446 (Siemens) which disclose the formation ofconduits by positioning of cylindrical plugs within heat-shrinkablesleeves.

Whilst some success may be achieved with the designs disclosed in GB2019114 and EP 0094793 problems have been experienced in fully sealingthe substrates at positions far inside the sleeve, at least underunfavourable conditions.

We have now discovered that such problems may be solved the use of aplug member in addition to a branch-off clip.

Thus, the invention provides a method of forming a branch-off sealbetween a heat-shrinkable sleeve and at least two spaced-apart elongatesubstrates, which comprises the steps of:

(a) positioning the substrates within the heat-shrinkable sleeve;

(b) positioning between the substrates and within the sleeve at an openend thereof, a plug having a larger cross-sectional size at a firstposition away from said open end and a smaller cross-sectional size at asecond position towards said open end;

(c) positioning a heat activatable sealing material at the firstposition;

(d) forming and/or maintaining at least three heat-shrinkable conduits(preferably terminal conduits, although a middle conduit need not extendto the extreme end of the sleeve) in the sleeve by positioning one ormore clips at the open end of the sleeve such that the substrates andthe plug are in respective conduits; and

(e) while the clip remains on the sleeve applying heat so as to affectshrinkage of the sleeve, to activate the sealant, and form the desiredseal.

The above steps may be carried out in any order, and the following orderis preferred. A sleeve is first installed around the substrates,preferably by wrapping it around them and securing it in thewrapped-around configuration. Next, the plug and sealant are placedwithin the sleeve between the substrates, placing of plug and sealantpreferably occurring simultaneously since the plug preferably includesthe sealant especially as a tape wrap around a support member. Then,preferably two clips are installed, respective clips being positionedbetween the plug and a respective substrate. Heat is then applied, forexample, by an open-flame torch or a hot-air gun or by electricalheating means that may be part of the sleeve, to cause the sleeve toshrink and the sealant to become heat-activated, preferably by meltingor otherwise softening. In a variation of this sequence, the plug andsealant may be positioned between the substrates and held in place bywedging or tape wrapping etc before positioning of the sleeve.

The clips may be two-legged clips of simple U-shape, each leg of the Ubeing positioned externally of the sleeve to bringcircumfrentially-spaced portions of the sleeve together and/or tomaintain such portions together (for example, where the sleeve ispre-shaped) during heat-shrinkage, and optionally also during servicelife of the product. Preferred clips, however, comprise three legs,preferably lying in a common plane, a middle leg of the clip comprisinga sealing material, preferably a hot-melt adhesive, and moreparticularly comprising a heat-conductive support coated with a sealingmaterial. Such a clip is positioned with its outer legs externally ofthe sleeve and its middle leg internally of the sleeve between thesubstrates. In this way sealing material is delivered by the clip to aspace that may otherwise remain between the substrates and the sleeve.Where the middle leg comprises a heat-conductive support and a sealingmaterial, heat may be conducted during installation from a torch etc viathe outer legs to the middle leg to activate the sealing materialthereon.

The plug may have any suitable shape so long as one end has a largercross-sectional size than the other end, these ends being defined in themethod of the invention in terms of their position relative to thesleeve when the plug is installed in the sleeve. We prefer, however thatthe plug be elongate and positioned substantially parallel to thesubstrates. Preferably the plug (or a support member thereof) is ofsubstantially uniform cross-sectional shape along its length, and alsois preferably of substantially circular or substantially ovalcross-section. In a particularly preferred embodiment the plug (or asupport member thereof) comprises first and second substantiallycylindrical portions interconnected by a substantially frustoconicalportion, the first portion being of larger cross-sectional size than thesecond portion. We prefer that the second portion is from 0.75-2.0,preferably 1.0-1.75 times the length of the first portion, and that thefrusto-conical portion (where present) is from 0.2-1.0, preferably0.2-0.5 times the length of the first portion. The first portionpreferably has a cross-sectional size in the direction from onesubstrate to the other of from 0.5-0.95 , more preferably 0.6-0.9 timesthe separation between the substrates. The plug may be built up inlength and/or cross-section in a modular fashion to adapt it todifferent sizes of substrate. For example, an adaptor of annular shape,comprising for example a sealing material, may be installed around thefirst portion to increase its cross-sectional size.

Where a cable splice case is to be sealed, the plug preferably has alength such that the first portion touches or almost touches (say, iswithin 2 or 3 cms) of the splice or splice case that joins or seals thetwo cables and the second portion extends to a position from 3 cms shortof to 3 cms proud of the end of the sleeve.

The heat-shrinkable sleeve may, for example, comprise a uniform extrudedpolymeric material or a composite material, preferably one comprising afibre-reinforced polymeric material. The fibres may be present as afabric, especially a woven fabric and may comprise heat-shrinkableand/or heat-stable fibres. In a preferred embodiment the sleeve hascircumferentially-extending heat-recoverable fibres andlongitudinally-extending heat-stable fibres, preferably comprisingpolyethylene and glass respectively. Such a composite material isdisclosed and claimed in EP 0116393 (Raychem) the disclosure of which isincorporated herein by reference.

The invention is further illustrated with reference to the accompanyingdrawings, in which: FIGS. 1 and 2 show prior art branch-off techniques;

FIG. 3 is a diagrammatic plan representation of components used in asealing method of the invention but with the heat-shrinkable sleeveomitted;

FIG. 4 shows a modular plug; and

FIG. 5 is an end view of an installed splice case made by the method ofthe invention.

The prior art clip 1 of FIG. 1 has two outer legs 2 and a middle leg,and is positioned at an end of a heat-shrinkable sleeve 4 to form twoterminal conduits 5. The clip causes deformation of the sleeve (which inthe absence of the clip had a single, larger, terminal conduit) to bringtogether circumferentially-spaced portions thereof at a position 6. Thisdesign is disclosed in U.S. Pat. No. 4,400,579, mentioned above.

A different design of prior art clip, having the form of a fork, isshown in FIG. 2, which is a transverse cross-section at the end of ashrinkable sleeve 4 surrounding two multi-core telecommunications cables7. The sleeve is a wrap-around sleeve, held in the wrapped-aroundconfiguration by a closure means 8. The clip or fork here has only twolegs and opposing portions of the sleeve 4 at position 6 between fixedspace-apart cables 7 are threaded through the legs, or prongs, of theclip 1. The two portions of the sleeve are thus held in contact with oneanother over a significant length 6. The sleeve is, or course, shownbefore shrinkage. This design is disclosed in GB 2019114, mentionedabove.

FIG. 3 is a plan view of an end of a cable splice case, showingpositioning of two branch-off clips and a plug, as used in theinvention, but the heat-shrinkable sleeve is omitted for clarity. Twocables 7 are spliced in a splice case 9, for example a lead splice inwhich the outlets 10 of the splice are spaced apart by a fixed distance.The incoming cables 7 are surrounded by one or more cable jackets 11. Itis often desirable that the region of the lead splice shown surroundedby a dotted line be environmentally protected by a sealing material inaddition to being surrounded by a sleeve. The sealing technique of FIG.1 is likely to be unable to deal easily with the great and fixedseparation between the outlets 10, and the technique of FIG. 2 whilst itcan seal a surrounding sleeve at its extremity is not in general able toprovide direct corrosion protection to the part of the splice casemarked.

In the invention a plug 12 is provided between the cables and within thesleeve. The plug 12 is provided between the cables and within thesleeve. The plug 12 comprises a first portion 13 of largercross-sectional size connected by a frusto-conical portion 14 to asecond portion 15 of smaller cross-sectional size, the frusto-conicalportion tapering towards the second portion.

Preferably the base of the frusco-conical portion is the same size andshape as those of the first portion, and its top is the same size andshape as those of the second portion so a smooth transition betweenfirst and second portions is provided. The first portion comprises asealing material, such as a hot-melt adhesive, which is shown bystippling. If desired, the sealing material may be supplied separately,for example by wrapping it around the cable outlets 10. The plug maycomprise a support member 12a, coated with a sealing material. Thesupport member may be heat-conductive to aid activation of the sealingmaterial. It is believed that the plug may serve to deliver the sealingmaterial to the desired location and may act as a dam, as well asreducing the amount of sealing material required.

FIG. 4 shows a modular plug in which the part 16 can be added to amember 12a to give a plug having a first portion 13 of increaseddiameter. The part 16 may comprises an annulus of sealing material inwhich the unit 12a is a support member for the sealing material.

FIG. 5 shows an end view of a splice case, which would correspond to theview 17 of the prior art splice case of FIG. 1. Here two clips 1 areused, on each side of the plug, whose second portion 15 can be seen. Thedotted line 19 shows the position of the first portion of the plug thatis hidden within the sleeve 4. Any gaps between the cables and thesleeve etc may be filled by a sealing material 18, for example from aninternal coating of the sleeve, from a middle leg 3 of the clips 1,and/or from the plug. Instead of two separate clips, a single clip maybe used, for example incorporating two structures similar to the twoclips illustrated.

We claim:
 1. A method of forming a branch-off seal between aheat-shrinkable sleeve and at least two spaced-apart elongatesubstrates, which comprises the steps of:(a) positioning at least twospaced-apart elongate substrates within a heat-shrinkable sleeve; (b)positioning between the substrates and within the sleeve at an open endthereof a plug having a larger cross-sectional size at a first positionaway from said open end and a smaller cross-sectional size at a secondposition towards said open end; (c) positioning a heat-activatablesealing material at the first position; (d) forming shrinkable conduitsin the sleeve by positioning one or more clips at the open end of thesleeve such that the substrates and the plug are in respective conduits;and (e) while the clip remains on the sleeve, applying heat so as toaffect shrinkage of the sleeve to activate the sealing material, andform the desired seal.
 2. A method according to claim 1, in which theplug comprises a support member having an adhesive tape wrapped aroundit at least at said first position, said adhesive tape providing atleast part of said sealing material.
 3. A method according to claim 1,in which three conduits are formed by a method which comprisespositioning at least two clips, each having at least two elongate legs,at the open end of the sleeve, respective clips being positioned betweenthe plug and a respective substrate wherein at least two legs of eachclip are positioned externally of the sleeve.
 4. A method according toclaim 3, in which each of said clips has at least three legs, at leastone leg comprising a heat activatable sealing material, said at leastone leg being positioned internally of the sleeve.
 5. A method accordingto claim 1, in which the plug or a support member thereof is ofsubstantially uniform cross-sectional shape along a length thereof.
 6. Amethod according to claim 1, in which the plug or a support memberthereof is of substantially circular or substantially ovalcross-section.
 7. A method according to claim 1, in which the plug or asupport member thereof comprises first and second substantiallycylindrical portions interconnected by a substantially frusto-conicalportion tapering towards the second portion, the first portion being oflarger cross-sectional size than the second portion.
 8. A methodaccording to claim 1, in which the sleeve comprises a compositematerial.
 9. A method according to claim 8, in which the compositematerial comprises a fibre-reinforced polymeric material.
 10. A methodaccording to claim 1, in which the substrates are spaced apart by afixed distance.
 11. A method according to claim 1, in which thesubstrates comprise cables.
 12. A method according to claim 11, in whichthe substrates comprise a lead cable splice.
 13. A kit of parts forcarrying out a method of forming a branch-off seal between aheat-shrinkable sleeve and at least two spaced-apart elongatesubstrates, the kit which comprises:a heat-shrinkable sleeve; a plughaving a larger cross-sectional size at a first portion away from anopen end of the heat-shrinkable sleeve and a smaller cross-sectionalsize at a second portion towards the open end, said plug being adaptedto fit between the spaced-apart elongate connectors; and a clip, saidclip shaped and formed so as to remain on the sleeve during theapplication of heat so as to affect shrinkage of the sleeve to activatea sealant and to form a plurality of shrinkable conduits surrounding thesubstrates and the plug at the second position, to activate heat sealingmaterial provided on at least the first portion of the plug and from thedesired seal.